1. Field of the Invention
This invention relates to an assembly construction for a sewing machine and more particularly it relates to an assembly construction for a sewing machine so designed that the presser and needle bar unit, loop taker unit, and work feeding mechanism and the components of various mechanisms including the operating mechanisms therefor can be easily assembled and adjusted.
2. Description of the Prior Art
An arrangement for a sewing machine is known in which the rear or front surface of the machine frame is opened to install various mechanism components.
For example, in U.S. Pat. No. 4,044,701 issued to Giesselmann et al. on Aug. 30, 1977, various mechanism components and devices in pre-assembled condition are mounted on seats formed in advance on the frame. It is also disclosed therein that the sewing machine is so arranged that these components can be adjusted for proper positioning during assembly operation. According to this U.S. patent, a great contribution is made to increasing the efficiency of assembly operation in that various mechanism components in pre-assembled condition are mounted on seats formed in advance on the frame.
In such assembly construction, however, it often occurs that in order to replace a component which is susceptible to damage and which requires frequent replacement, some main mechanism components must be loosened and removed before the replacement operation can be performed. The reason is that such components requiring frequent replacement are attached to the frame prior to the main mechanism components. Examples of the components requiring frequent replacement are operating mechanism components including dials and levers which are most frequently manipulated by the sewer and which are liable to be damaged because they are mounted partly exposed beyond the machine frame, and the hook point of the loop taker liable to be damaged by the needle during sewing operation. The operation of loosening and removing main mechanism components simply to replace a damaged component is troublesome, as described above, moreover, this operation results in disturbing the proper positional relation between mechanism components, so that readjustment is required after replacement. Further, functional adjustment of the sewing machine subsequent to completion of assembly operation is very troublesome since it involves adjusting the relative positions of mechanism components from the rear side while manipulating the operating members disposed on the front of the machine and connected to various mechanism components.
U.S. Pat. No. 4,193,361 issued to Johnson on Mar. 18, 1980 discloses an assembly method wherein a frame entirely opened in the front is formed with seats machine-finished to the same level and various mechanism components are mounted on these seats. This method is very advantageous in that it eliminates the cumulative errors in mounting dimensions between components in the conventional frame, which errors result from the fact the seats for mounting components differ in height according to the shape and size of these components.
With this assembly construction, however, the advantage of the seats for mounting components being flush with each other is attended with limitations on the shape and size of components, complicating the shape of components.
Further, this Johnson patent also discloses that all of the driving mechanism components and operating mechanism components, which are housed in or held by the frame, are divided substantially into two groups, one associated with the arm shaft and the other with the bottom arm shaft, for general unitization purposes.
In assembling these two generally unitized subassemblies, however, there is no denying that substantially the same number of operating steps and the same amount of operating time are involved as in the conventional sewing machine. Further, the handling, such as transfer, of the subassemblies is inconvenient. For these reasons, the assembly construction of Johnson patent cannot absolutely be said to be advantageous.